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Biomedical subjects

K J Mann

Publications and source records attributed to K J Mann.

At least 19 recordsLinked to original sources
PubMed2001

Differential effect of 1,10-phenanthroline on mammalian, yeast, and parasite glycosylphosphatidylinositol anchor synthesis.

Glycosylphosphatidylinositol (GPI) anchoring of proteins to the plasma membrane is a common mechanism utilized by all eukaryotes including mammals, yeast, and the Trypanosoma brucei parasite. We have previously shown that in mammals phenanthroline (PNT) blocks the attachment of phosphoethanolamine (P-EthN) groups to mannose residues in GPI anchor intermediates, thus preventing the synthesis of mammalian GPI anchors. Therefore, PNT is likely to inhibit GPI-phosphoethanolamine transferases (GPI-PETs). Here we report that in yeast, PNT also inhibits the synthesis of the GPI anchor as well as GPI-anchored proteins. Interestingly, the mechanism of PNT inhibition of GPI synthesis is different from that of YW3548, another putative GPI-PET inhibitor. In contrast to mammals and yeast, the synthesis of GPIs in T. brucei is not affected by PNT. Our results indicate that the T. brucei GPI-PET could be a potential target for antiparasitic drugs.

Animals↗
PubMed2001

1,10-Phenanthroline inhibits glycosylphosphatidylinositol anchoring by preventing phosphoethanolamine addition to glycosylphosphatidylinositol anchor precursors.

The glycosylphosphatidylinositol (GPI) moiety is widely used to anchor a functionally diverse group of proteins to the plasma membrane of eukaryotes. In mammals, the predominant glycan structure of the GPI anchor consists of EthN-P-Man-Man-(EthN-P)Man-GlcN attached to an inositol phospholipid. In a smaller percentage of anchors analyzed to date, a third P-EthN group linked to the middle mannosyl residue was found. The transfer of the three P-EthN groups present in the GPI glycan core is likely to be carried out by three different GPI-phosphoethanolamine transferases (GPI-PETs). Here we report that 1,10-phenanthroline (PNT), a commonly used inhibitor of metalloproteases, is a novel inhibitor of GPI anchor synthesis. Addition of PNT to cells caused the accumulation of GPI anchor intermediates that are substrates for GPI-PETs, suggesting that these enzymes are the targets of PNT. ZnCl(2) blocked the effect of PNT, a known Zn chelator, and Zn itself was able to stimulate the GPI anchor synthesis, indicating that this cation is likely to be required for GPI-PET activity. PNT acutely inhibited the synthesis of GPI-anchored proteins, but the synthesis was rapidly restored once the inhibitor was washed out. Therefore, PNT will be a useful tool to study the metabolism and trafficking of GPI anchor intermediates by providing a switch to turn the pathway on and off.

Alkaline Phosphatase↗
PubMed1999

Glycosylphosphatidylinositol-anchor intermediates associate with triton-insoluble membranes in subcellular compartments that include the endoplasmic reticulum.

Glycosylphosphatidylinositol (GPI)-anchored proteins are resistant to solubilization with Triton X-100 at 4 degrees C, and they can be recovered in Triton-insoluble membranes (TIMs) that float to a characteristic buoyant density. Because the GPI structure itself has been shown to target GPI-anchored proteins to TIMs, we investigated the association of GPI-anchor intermediates with TIMs. GPI-anchor biosynthesis involves a pathway of some 10 steps that take place in the endoplasmic reticulum (ER). These intermediates include glucosaminyl-acylphosphatidylinositol [GlcN-(acyl)PI] and later mannosylated GPIs, denoted H6, H7 and H8, that are present not only in the ER but also in other cell compartments, including the plasma membrane. At least two-thirds of the GlcN-(acyl)PI in HeLa D cells and mannosylated GPIs in K562 cells were found in TIMs. Although previous reports have considered TIMs to be derived primarily from the plasma membrane, we recovered TIMs from subcellular fractions enriched in ER membranes. The ER marker calnexin and GPI-anchored proteins as well as N-acetylglucosaminyl-phosphatidylinositol and mannosylated GPIs were present in ER-TIMs. Interestingly, GlcN-PI and H7 were less enriched in ER-TIM than the other GPIs, suggesting that ER-TIMs might reflect a compartmentalization of the GPI-anchor biosynthetic pathway in the ER.

Animals↗
PubMed1998

Association of ceramide accumulation with photodynamic treatment-induced cell death.

Ceramide, a stress-induced second messenger, has been associated with apoptosis in several malignant and non-malignant cell lines. We have shown that photodynamic treatment (PDT), using the phthalocyanine photosensitizer Pc 4 (HOSiPcOSi[CH3]2[CH2]3N[CH3]2), causes increased ceramide generation and subsequent induction of apoptosis in L5178Y-R (LY-R) mouse lymphoma cells. To test further if ceramide generation accompanies photocytotoxicity, we treated various cell lines with a PDT dose producing a 99-99.9% loss of clonogenicity. Like LY-R cells, human leukemia (U937) cells underwent rapid DNA fragmentation initiating within 1 h after PDT. Similarly, Chinese hamster ovary (CHO) cells showed rapid DNA laddering, beginning 1 h following the treatment. In contrast, mouse radiation-induced fibrosarcoma (RIF-1) cells showed no apoptosis within 24 h post-PDT, as judged by the absence of 50 kbp and oligonucleosome size DNA fragments, as well as no annexin V binding to cells with preserved membrane integrity. Using the same doses of PDT, we observed a time-dependent ceramide accumulation in all three cell lines. While a significant increase in ceramide levels was reached within 1 and 10 min in U937 and CHO cells, respectively, elevated ceramide production was measured only after 30 min in RIF-1 cells. In addition, exogenous N-acetyl-sphingosine was able to mimic PDT-induced apoptosis in U937 and CHO cells. We suggest that ceramide accumulation is associated with PDT-induced apoptosis and photocytotoxicity.

Animals↗
PubMed1997

The home as a framework for health care.

The past two or three decades have witnessed a steep rise in the cost of health and social services. It is anticipated that this uphill climb will continue and bring these systems to a complete collapse within a few decades. The prevention of this crisis depends on the elimination of some of the causes of the rise: (a) we do not want to save costs by sacrificing the quality of our services; (b) we have no control over the quantity of clients utilizing these services, or the seriousness of their problems; (c) we can, however, replace part of the expensive institutional care by the more natural and cost-effective home care, supplied by volunteers, strengthened by human and technological services. These principles guided an Israeli organization called Yad Sarah, whose leadership in the supply of home and community care enables thousands of ill, elderly and disabled people to remain at home and thus save the high cost of institutionalization.

Aged↗
PubMed1992

Acute renal denervation decreases tubular phosphate reabsorption.

Acute renal denervation (DNX) has been reported to increase urinary phosphate (Pi) excretion in rats with intact parathyroid glands and also in rats which were thyroparathyroidectomized (TPTX). The present study was performed to determine the effects of acute renal denervation on the tubular transport of Pi in rats in the absence of parathyroid hormone (PTH) and in rats with constant PTH levels. In TPTX rats, the reabsorbed Pi normalized for the glomerular filtration rate (Reab Pi/GFR) was 2.38 +/- 0.16 mumol/ml in the DNX kidney compared to 2.56 +/- 0.16 mumol/ml (p < 0.05) in the contralateral innervated (INN) kidney at endogenous plasma phosphate levels (n = 6). The lower values for the Reab Pi/GFR in the DNX kidney persisted at elevated plasma phosphate concentrations during phosphate infusions. Infusion of PTH resulted in markedly lower Reab Pi/GFR values in the innervated kidney (1.47 +/- 0.21 mumol/ml) at endogenous plasma phosphate levels than in the vehicle-infused group. Furthermore, the Reab Pi/GFR in the DNX kidney was decreased (1.21 +/- 0.14 mumol/ml, n = 6) compared to the contralateral INN kidney. These studies demonstrate that acute renal DNX decreases the tubular transport of Pi both in the absence and in the presence of constant PTH levels.

Absorption↗
PubMed1991

Renal denervation enhances the phosphaturic effect of parathyroid hormone.

Hyperventilation/hypocapnia increases renal phosphate reabsorption and decreases the phosphaturic effect of parathyroid hormone (PTH). Recent studies suggest that the blunted phosphaturic effect of PTH in hyperventilated/hypocapnic rats may be mediated by the stimulation of renal beta-adrenoreceptors. In the present study, no differences in plasma catecholamine levels were detected in hyperventilated/hypocapnic rats as compared to hyperventilated/normocapnic rats. Therefore, studies were performed to determine the role of the renal nerves in the blunted phosphaturic effect of PTH in hyperventilated/hypocapnic rats. In clearance experiments in acutely thyroparathyroidectomized male Sprague-Dawley rats, PTH infusion increased the fractional excretion of phosphate (FEPi) in the denervated left kidney of hyperventilated/hypocapnic rats (n = 8), from 2.4 +/- 1.1 to 18.6 +/- 2.7%, as compared to 1.0 +/- 0.3 to 9.1 +/- 2.1% in the contralateral innervated kidney. Denervation of the left kidney in hyperventilated/normocapnic rats (n = 8) also significantly increased the phosphaturic response to PTH by 2.5 +/- 1.5 to 26.9 +/- 3.0% as compared to 0.9 +/- 0.5 to 18.6 +/- 2.6% in the contralateral innervated kidney. The phosphaturic responses to PTH were similar when comparing the denervated kidney in hyperventilated/hypocapnic rats with the innervated kidney of hyperventilated/normocapnic rats. Thus, renal denervation enhanced the phosphaturic effect of PTH in both hyperventilated/hypocapnic and hyperventilated/normocapnic rats. These results suggest that renal nerves play a role in the modulation of the phosphaturic effect of PTH.

Animals↗
PubMed1985

Recommendations for the formulation of the Nursing Care Insurance Law.

In Israel, old-age pensions for men aged greater than or equal to 70 years and women aged greater than or equal to 65 years are provided by the National Insurance Institute. A supplementary allowance is given when the pension is the sole income. However, in 1980 these benefits were recognized as insufficient in cases of functional incapacity, so a change in the existing National Insurance Law was considered necessary. A national committee was appointed to formulate the Nursing Care Insurance Law, which would extend the activities of the National Insurance Institute. Monies were to be allocated for personal care, home maintenance, assistance to families and community services. Home care was considered preferable to institutionalization for psychological and social reasons; however, institutionalization was recognized as necessary when home care is no longer feasible in cases of total dependence and illness. Regional Committees and a Central National Committee will be established for planning and supervision. Government surveys were used to determine the percentage of the aged needing help, according to which the overall budget is to be calculated. The Nursing Care Insurance Law was passed in 1983, but so far no agreement has been reached concerning the distribution of monies.

Aged↗
PubMed1974

Integration of family medicine into university teaching hospital in Israel: a pilot project.

In accordance with the recommendation of the Mann Committee established by the Israel Medical Association a centre for family medicine serving 11 villages was established at Beit Shemesh, Israel, in 1970; this was affiliated with the department of internal medicine at Hadassah University Hospital. The centre's doctors have become fully-fledged members of the department, and have full access to its resources and participate actively in its service, teaching, and research activities. They teach family medicine to students at the Hebrew University-Hadassah Medical School and have the same academic responsibilities and privileges as all other faculty members. This affiliation has raised the standard of the health service provided.

Community Health Services↗